A gas turbine engine may be used to supply power to various types of vehicles and systems. For example, gas turbine engines may be used to supply propulsion power to an aircraft. Many gas turbine engines include at least three major sections, a compressor section, a combustor section, and a turbine section. The compressor section receives a flow of intake air and raises the pressure of this air to a relatively high level. In a multi-spool (e.g., multi-shaft) engine, the compressor section may include two or more compressors. The compressed air from the compressor section then enters the combustor section, where a ring of fuel nozzles injects a steady stream of fuel. The injected fuel is ignited by a burner, which significantly increases the energy of the compressed air.
The high-energy compressed air from the combustor section then flows into and through the turbine section, causing rotationally mounted turbine blades to rotate and generate energy. The air exiting the turbine section is then exhausted from the engine. Similar to the compressor section, in a multi-spool engine the turbine section may include a plurality of turbines. The energy generated in each of the turbines may be used to power other portions of the engine.
In addition to providing propulsion power, a gas turbine engine may also be used to supply either, or both, electrical and pneumatic power to the aircraft. For example, in the past some gas turbine engines include a bleed air port between the compressor section and the turbine section. The bleed air port allows some of the compressed air from the compressor section to be diverted away from the turbine section, and used for other functions such as, for example, main engine starting air, environmental control, and/or cabin pressure control. More recently, however, gas turbine engines are being designed to not include bleed air ports. This is in response to a desire to more fully utilize electrical power for main engine starting air, environmental control, and cabin pressure control. Thus, instead of using bleed air to support these various functions, the high pressure turbine may be used to drive one or more electrical generators to supply electrical power to support these functions.
Accordingly, the next generation of aircraft may be more electric in architecture. This reliance on electric power may increase the generator load and therefore shaft horsepower (SHP) extraction load on the high pressure (HP) spool of the propulsion engine (SHP load/thrust ratio is increasing). As a result, the engine may not be able to keep up with the generator load demand at various low thrust conditions in the flight envelope. As a result, the engine may be required to run at high core speeds and surge bleed to reduce engine thrust.
In a typical turbine engine, the turbine drive system (TDS) may extract pneumatic power from the aircraft bleed air system, including surge bleed, convert it into mechanical power and supply the power back into the engine accessory gearbox via a rotating shaft. This process in effect may off-set a portion of the electrical load. The generation of this mechanical power may provide gearbox power assistance during periods of engine operation throughout the engine operating speed range. During aircraft operation, peak power from the TDS may typically be demanded at speeds ranging from idle to maximum power (roughly between 60-100% engine speed). This power assistance may offset engine core power required to drive a number of engine accessory gearbox mounted accessories (generators, pumps, etc.). The TDS may be powered by a controlled supply of pneumatic energy from the engine itself (high, low, or intermediate stage, etc.) or from an external source such as an auxiliary power unit (APU), ground power unit (GPU), or another engine, via the aircraft's pneumatic distribution system.
The TDS requires both mechanical fixation when in the energized mode (TDS control valve open) and mechanically disengagement when deenergized. More specifically, when energized, the TDS must be capable of responding to fast changes in engine speed (engine accelerations/decelerations, i.e. Bode's) which is best served by a mechanically fixed turbine drive. When not energized, the TDS must be capable of mechanically disengagement to allow the drive turbine to come to rest. This mechanical disengagement may result in the prevention of turbine overheating, and wear with respect to bearings, gears and seals in the TDS, and improve engine performance.
Hence, there is a need for a TDS that is capable of responding to engine accelerations and decelerations when required via mechanical engagement to the engine core and disengagement when not in use. The system should not significantly reduce engine efficiency, and/or significantly increase fuel consumption, and/or increase overall operational costs. The present invention addresses one or more of these needs.